Other reasons

>first, it's extremely hard to define 'a Debian install'.

In my opinion it isn't. Every combination of software that is in a distributions 'main' is a
valid Debian install.

>Second, Debian systems tend to be more customized (less standardized) than other
installations of other distro's.

Almost all software debian distributes comes with proper 'out of the box' defaults. Anything
less standardized is put there explicitly.

> the release cycle is slooooowwww. 

It's just about adequate for corporate use I'd say . When stuff works, you really don't want
to touch it anymore. Debian "Stable" actually means "no regressions"; there's a reason for
that.

>Debian is created from a very conservative standpoint. The base system is guaranteed to run
on very modest hardware. While this is a good thing, businesses won't care. Their hardware
will almost never be older than 4 years.

Hardware that is stable and does the thing it was purchased for usually runs until the magic
smoke escapes.

>From a political point of view, Debian is completely right: Be Free!

From a business perspective they're right as well. When one finally needs to upgrade to a
newer version of the os, since the old version is no longer supported, debian is king. The
chances of a flawless upgrade are a lot larger when the entire system being upgraded consists
only of free software. And flawless upgrades result in less downtime.

Most of your criticisms are valid from a single end-user perspective and actually support a
business-case for using debian.
The only exceptions I can think of righ now are developer desktops, which tend to track the
latest hardware and businesses who have need of non-free software.

The only valid anti-business point you make is the unpredictable release cycle. It's why smart
businesses have competent in-house staff to keep tabs on debian, or hire someone who does.

>Debian is a very good distribution, for its purpose. But its purpose isn't to be used in a
corporate environment. 

Its purpose is to be a universal operating system, including the corporate environment, and it
is pretty succesful fulfilling that role.

>and an excellent basis for more business-like distributions like Ubuntu.

Maybe Debian lacks hype and friendly faces, but apart from these sales assets Ubuntu is just a
Debian that breaks down a lot (relatively). And 'breaks down a lot' is exactly the sort of
thing that serious businesses are trying to avoid.